I was out on my yacht motoring along for 20 mins when the engine
(yanmar 3QM30h) began to loose power, unresponsive to throttle, then stalled. Luckily I was not in a seaway, no wind
or drift to contend with. I suspected fuel
starvation as the problem. Both the 70 Litre tanks
were 75% full, I was drawing from the port tank with fuel
return going to starboard. Engine
would turn over normaly on starter so not siezed. I had a look at the primary filter and found it nearly dry. Switched over to starboard tank with fuel return to still to starboard. Bled the engine's fuel system and engine started easily, no more problems for the remainder of the day. Back on the mooring
rechecked port tank, plenty of fuel, switched back to port tank and ran the engine under load for 30 min with no stalling.
Thoughts - Having the fuel return going to opposite tank set up a pressure vacuum in the port tank thus defeating the fuel pumps effort to lift
fuel? Is this possible considering each tank has a breather pipe?
Gunk in the tank temperarily blocked the fuel pick up line? It was in dead calm that I was motoring so no fuel sloshing about, recent fuel samples drawn from bottom of each tank appeared clean?
Any advice would be welcome.